diff --git a/config.h.win32 b/config.h.win32
index 44ebffec15..52c53ffc70 100644
--- a/config.h.win32
+++ b/config.h.win32
@@ -375,17 +375,6 @@ typedef __int64 off_t;
 @HAVE_KRB5_H@
 @HAVE_KRB5_KRB5_H@
 
-/*
- * Define to nothing if C supports flexible array members, and to 1 if it does
- * not. That way, with a declaration like `struct s { int n; double
- * d[FLEXIBLE_ARRAY_MEMBER]; };', the struct hack can be used with pre-C99
- * compilers. When computing the size of such an object, don't use 'sizeof
- * (struct s)' as it overestimates the size. Use 'offsetof (struct s, d)'
- * instead. Don't use 'offsetof (struct s, d[0])', as this doesn't work with
- * MSVC and with C++ compilers.
- */
-#define FLEXIBLE_ARRAY_MEMBER /**/
-
 /* Avoid warnings with strlen() */
 #ifdef _WIN64
 #define strlen(x)	(unsigned int) strlen(x)
diff --git a/configure.ac b/configure.ac
index 2a5a9b4c51..a1787adf66 100644
--- a/configure.ac
+++ b/configure.ac
@@ -328,7 +328,6 @@ AX_TLS([AS_IF([test "$ac_cv_tls" != "thread_local"],
 AC_C_CONST
 AC_C_INLINE
 AC_C_VOLATILE
-AC_C_FLEXIBLE_ARRAY_MEMBER
 
 #
 # Check for yield support on ARM processors
diff --git a/lib/dns/client.c b/lib/dns/client.c
index 7a68623ca2..a86a5da468 100644
--- a/lib/dns/client.c
+++ b/lib/dns/client.c
@@ -3061,7 +3061,7 @@ typedef struct {
 	dns_rdata_t rdata;
 	size_t size;
 	isc_mem_t *mctx;
-	unsigned char data[FLEXIBLE_ARRAY_MEMBER];
+	unsigned char data[];
 } dns_client_updaterec_t;
 
 isc_result_t
diff --git a/lib/isc/ht.c b/lib/isc/ht.c
index b3c9e5100d..7bda1cf662 100644
--- a/lib/isc/ht.c
+++ b/lib/isc/ht.c
@@ -29,7 +29,7 @@ struct isc_ht_node {
 	void *value;
 	isc_ht_node_t *next;
 	size_t keysize;
-	unsigned char key[FLEXIBLE_ARRAY_MEMBER];
+	unsigned char key[];
 };
 
 struct isc_ht {